Organic semiconductor materials are subdivided into hole and electron transport materials. They are needed for the manufacturing of organic electronic components, such as organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and/or organic solar cells.
On the side of hole transport materials, very efficient and stable structures have been developed in the last 15 years which, depending on the application with the most varied hole injection characteristics, are available and, in the hole-transporting, oxidized state, form stable radical cations.
On the side of electron transport materials, there have been up to now only very few representatives which meet the high requirements for electron transport materials for organic electronics. At present, the derivatives of phenanthrolin (BCP and BPhen) and derivatives of oxadiazole are considered good electron conductors. Radical-anionic species, which are formed during the operation of these components, bring about a configuration change in the heterocyclic structures, so that the electron transport characteristic declines as a consequence of the formation of conjugation interruptions.
The known materials exhibit deficits both in the bandwidth of the electron injection and also in their stability in the electron-transporting, reduced state, so that, in particular, the radical anions cannot be formed reversibly over a longer time period.
As a rule, the semiconducting characteristics of the materials are attained by doping, because the base materials alone are never conductive enough.